Apparatus and methods for self-heating burn-in processes

ABSTRACT

A method includes installing a device under test (DUT) into each of a plurality of burn-in boards. The method further includes docking each of the burn-in boards to a respective docking location, each of the burn-in boards with a single respective DUT installed therein. The method further includes subjecting the DUTs to a self-heating burn-in procedure while the burn-in boards are docked to the docking locations. Other embodiments are described and claimed.

BACKGROUND

“Burn-in” is a test procedure commonly applied to integrated circuit(IC) devices in which the devices are exercised at elevated temperatureto determine whether defects are present in the devices. Typically,burn-in is applied only to a sample of a lot of devices that have justbeen manufactured. In conventional burn-in techniques, each device to beburned-in (sometimes referred to as a “device under test” or “DUT”) isinstalled in a socket in a burn-in board. A typical burn-in board mayhave 15 or more sockets, each containing a DUT during the burn-in.

Once the DUTs have been installed in the sockets of the burn-in board,the burn-in board is placed in an oven, typically in company with otherburn-in boards having installed therein other DUTs of the sample ofdevices being burned-in. The oven is then heated to the target burn-intemperature (e.g., 100° C.) and patterns of drive signals are applied tothe DUTs via the burn-in boards during the burn-in period (of, e.g., 30minutes). The DUTs are monitored during the burn-in and/or tested afterburn-in to determine whether the DUTs have failed during burn-in. Afterthe burn-in period is complete, the oven is allowed to cool to roomtemperature, and the burn-in boards are then removed from the oven.Thereafter, the DUTs are de-installed from the sockets of the burn-inboards, and passed to the next stage of test/manufacture.

Because of cycle time required for populating burn-in boards with DUTsand removing the DUTs from the burn-in boards, loading and unloadingburn-in boards to/from the oven, and heating and cooling of the oven,the actual elapsed time to provide a 30 minute burn-in may be severalhours. Also, burn-in ovens may occupy a substantial amount of factoryfloor space.

To overcome these and other disadvantages of conventional burn-in, thepresent inventor, with another, proposed a “self-heating burn-in”procedure in which the heating of the DUTs from room temperature to thetarget burn-in temperature results entirely from electrical powerdissipation within the DUTs themselves. In other words, no oven isrequired for “self-heating burn-in”. The present inventor has nowrecognized possible improvements in self-heating burn-in procedures.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic perspective view of a system provided according tosome embodiments to perform self-heating burn-in of DUTs.

FIG. 2 is a simplified block diagram of a DUT having design-for-test(DFT) features provided according to some embodiments.

FIG. 3 is a partly schematic, partly block diagram showing details ofDFT features of the DUT of FIG. 2.

FIG. 4 is perspective view of a burn-in board provided according to someembodiments.

FIG. 5 is a block diagram representation of the burn-in board of FIG. 4.

FIG. 6 is a schematic side cross-sectional view of a column of dockinglocations for docking burn-in boards in the system of FIG. 1.

FIG. 7 is a block diagram representation of a driver circuit that ispart of the system of FIG. 1.

FIG. 8 is a block diagram showing a controller and other portions of thesystem of FIG. 1.

FIG. 9 is a perspective view of a robot end effector used in the systemof FIG. 1.

FIG. 10 is a flow chart that illustrates a process for performing aburn-in procedure in the system of FIG. 1.

FIG. 11 is a schematic plan view of a system provided according to someother embodiments to perform self-heating burn-in of DUTs.

FIG. 12 is a partial isometric view of a tier of burn-in stations thatis part of the system of FIG. 11.

FIG. 13 is a partial isometric view of tiers of burn-in stations thatmay be part of the system of FIG. 11 according to some other embodiments

FIG. 14 is a schematic isometric view of a robot end effector that maybe used in the system of FIG. 11.

FIG. 15 is a schematic plan view of the robot end effector of FIG. 14

FIG. 16 is a view similar to FIG. 15 showing an alternative embodimentof the robot end effector of FIGS. 14 and 15.

FIG. 17 is a schematic side view of the robot end effector of FIGS. 14and 15.

FIG. 18 is a schematic plan view of a staging tray for DUTs that is partof the system of FIG. 11.

FIG. 19 is a schematic side view showing the end effector of FIGS. 14and 15 interacting with a burn-in station of the system of FIG. 11.

FIG. 20 is a flow chart that illustrates a process for performing aburn-in procedure in the system of FIG. 11.

FIG. 21 is a block diagram representation of a computer system that mayinclude a device like the DUT of FIGS. 2 and 3.

DETAILED DESCRIPTION

FIG. 1 is a schematic perspective view of a system 100 providedaccording to some embodiments to perform self-heating burn-in of DUTs.

The system 100 includes a plurality of vertical support structures 102arranged at various radial positions around a robotic arm 104 which isalso part of the system 100. The support structures may be, for example,walls and/or vertically oriented frames. The support structures may eachhave mounted thereon columns of docking locations (shown, e.g., in FIG.6, not separately shown in FIG. 1) to each of which a burn-in board 106is or may be docked. In some embodiments, each support structure 102 maysupport three columns of eight docking locations each, as indicated inthe drawing. In other embodiments, different numbers of columns persupport structure, and/or different numbers of docking locations percolumn may be provided. The number of support structures in the system100 may be more or fewer than the five support structures shown in thedrawing. As seen from FIG. 1, each docking location may face the roboticarm 104 and thus may face radially inwardly.

In some embodiments, as discussed in more detail below, each burn-inboard 106 may have one and only one socket (not separately shown inFIG. 1) to receive and hold a DUT (which may be a packaged IC or othersemiconductor device). In some embodiments, each docking location has arespective burn-in board docked to it virtually all the time, exceptwhen the burn-in board is away from the docking location to allow aprocessed DUT (i.e., a DUT for which the burn-in process has beencompleted) to be replaced with new DUT upon which burn-in is to beperformed. In some embodiments, for each burn-in board, a burn-inprocedure is taking place for the DUT currently held in the socket ofthe burn-in board virtually all the time that the burn-in board isdocked to the docking location. Consequently, the utilization of theburn-in boards may be highly efficient, since each burn-in board isactually engaged in burning in DUTs a high percentage of the time, withlittle down-time.

The system 100 may also include an installation station 108 which isaccessible by the robotic arm 104. As described further below, theinstallation station 108 may be operative to de-install a processed DUTfrom a burn-in board presented to the installation station, and toinstall a new DUT in the burn-in board.

There may also be included in the system 100 a number of tray holders110 which hold trays of processed and to-be-processed DUTs. (The traysare not separately indicated, but some DUTs are schematically indicatedat 112.) In some embodiments, the tray holders may be suitable forholding stacks of trays that comply with JEDEC (Joint Electron DeviceEngineering Council) standards. In some embodiments, there may be seventray holders (as indicated in the drawing) to perform the followingfunctions:

Tray holder no. 1: DUTs to-be-processed from a first lot of DUTs.

Tray holder no. 2: DUTs, from the first lot, that were burned-insuccessfully.

Tray holder no. 3: DUTs, from the first lot, that failed during burn-in.

Tray holder no. 4: DUTs to-be-processed from a second lot of DUTs.

Tray holder no. 5: DUTs, from the second lot, that were burned-insuccessfully.

Tray holder no. 6: DUTs, from the second lot, that failed duringburn-in.

Tray holder no. 7: empty trays.

As will be appreciated by those who are skilled in the art, the term“lot” as used herein refers to a group of IC devices that are producedin a single production run. Thus, the two lots referred to above areunderstood to have been produced in separate production runs and/or atdifferent times.

(The order in which the tray holders are listed above need notcorrespond to an order in which the tray holders are physicallypositioned in the system 100.)

It will be understood that the tray holders are positioned so as to beaccessible by the robotic arm 104.

FIG. 2 is a simplified block diagram of a typical one of the DUTs 112.The DUT 112 may incorporate design-for-test (DFT) features providedaccording to some embodiments. In actual physical appearance (notrepresented in the drawings) the DUT 112 may resemble a conventionalpackaged IC, notwithstanding the novel features incorporated therein asdescribed below. In addition to features described below, the DUT mayhave conventional IC device features such as those of a microprocessor,a memory controller hub, a memory device, a graphics chip, etc.

As seen from FIG. 2, the DUT 112 may further include a thermal sensingcircuit 202, a clock generation and selection block 204, core logic 206and a state machine 208. The thermal sensing circuit 202 detects theinternal temperature of the DUT. Based on the internal temperature, thethermal sensing circuit 202 sends one or more signals to the clockgeneration and selection block 204 to select a clock signal at anappropriate frequency. The core logic 206 may include a considerablenumber of logic gates (to implement conventional functions of thedevice) and may receive the selected clock signal provided by the block204 to operate at the frequency of the selected clock signal. The statemachine 208 may control the core logic 206 during burn-in to run varioustest modes.

As indicated at 210 in FIG. 2, the signal or signals provided by thethermal sensing circuit 202 to the clock generation and selection block204 may also be taken out to a terminal pin or pins 212, so that thesignal(s) from the thermal sensing circuit 202 may be receivedexternally from the DUT 112. At other terminal pins 214 input signals(e.g., clock signals of mutually different phases) for the clockgeneration and selection block 204 may be received from off the DUT.Also, a control signal or signals to trigger the state machine 208 maybe received from off the DUT at terminal pin(s) 216.

FIG. 3 shows some details of the thermal sensing circuit 202 and theclock generation and selection block 204 as provided according to someembodiments. As will be understood from subsequent discussion, thecircuitry shown in FIG. 3 may function as on-die temperature controlcircuitry to aid in controlling a self-heating burn-in mode of the DUT.The circuitry of FIG. 3 may constitute a portion of the DFT circuitry ofthe DUT.

As seen from FIG. 3, the clock generation and selection block 204includes an exclusive OR (XOR) gate 302, a multiplexer 304, and an ANDgate 306. The thermal sensing circuit 202 includes a number of fuses 308and an on-die thermal sensor 310.

The XOR gate 302 receives two clock signals which may be of the samefrequency (e.g., 10 MHz) but with mutually different phases (e.g.,shifted by 90° from each other). The input clock signals for the XORgate 302 may be provided from the burn-in board or from an externaldriver circuit (not shown in FIG. 3) which is discussed below. Thefrequency of the input clock signals may vary depending on the targetburn-in temperature and time.

Using the two phase-shifted clock signals, the XOR gate 302 generates aclock signal 312 which has a frequency that is twice the frequency ofthe input clock signals. For example, in one embodiment, if the inputclock signals are at 10 MHz with a 90° phase shift, then the outputclock signal 312 from the XOR gate 302 is at 20 MHz. The output clocksignal 312 and one of the input clock signals are both provided asinputs to the multiplexer 304. The multiplexer 304 selects a clocksignal out of the two clock signals input thereto in response to asignal 314 from the thermal sensing circuit 202. (In some embodiments,more than two clock signals, all at different frequencies, may beprovided to the multiplexer 304 for the multiplexer to select amongbased on a signal from the thermal sensing circuit 202.)

In one embodiment, the fuses 308 may include five programmable fusescoupled to the thermal sensor 310. The fuses 308 may be programmable todifferent temperature levels. The fuses 308 may be programmed duringwafer level sort testing of the DUT to set a target burn-in temperature.In one embodiment, the target burn-in temperature may be in the range90-100° C. It should be understood that the target burn-in temperaturemay vary in different embodiments, depending on a variety of factors,such as process variations, burn-in time, etc. Also, the DUT may includeadditional fuses programmed to set more than one temperature level.

In one embodiment, the fuses 308 provide the programmed target burn-intemperature to the thermal sensor 310. The thermal sensor 310 senses theinternal temperature of the DUT and compares the sensed temperature withthe programmed burn-in temperature. In response to the comparison, thethermal sensor 310 generates a number of output signals. In oneembodiment, the output signals of the thermal sensor 310 include thesignal 314 (which may be considered to be a “too hot” signal) toindicate that the sensed internal temperature of the DUT exceeds thetarget temperature. In one embodiment, the thermal sensor 310 furthergenerates a backup signal 316 that is asserted in the event that thesensed internal temperature of the DUT exceeds the target temperature bya certain amount (e.g., 10 or 12° C. in some embodiments). Signal 316may be considered a “catastrophic” signal.

In one embodiment, the “too hot” signal 314 is provided to themultiplexer 304 to select a clock signal for the core logic (FIG. 2, notshown in FIG. 3). When the internal temperature of the DUT is below thetarget temperature, it may be desirable to run the DUT at a higherfrequency to generate more heat in order to raise the internaltemperature to the target temperature. On the other hand, when theinternal temperature of the DUT is above the target temperature, it maybe desirable to run the DUT at a lower frequency to generate less heat.For example, in one embodiment, the multiplexer 304 selects the 10 MHzclock signal for the core logic when the signal 314 from the thermalsensor 310 indicates that the internal temperature of the DUT exceedsthe target temperature, and the multiplexer 304 selects the 20 MHz clocksignal for the core logic when the signal 314 indicates that theinternal temperature of the DUT does not exceed the target temperature.The selected clock signal from the multiplexer 304 and the“catastrophic” signal 316 are provided as inputs to the AND gate 306.

By selecting between the higher and lower clock frequencies duringburn-in, the temperature control circuitry of FIG. 3 may be able to varythe power dissipated by the DUT during burn-in by about 10 watts. Bytoggling back and forth between the two clock frequencies, thetemperature control circuitry may be able to stabilize the DUT internaltemperature at the target burn-in temperature. However, for some devicesthe power range may exceed the capabilities of the temperature controlcircuitry to stabilize the temperature just by frequency toggling.Consequently, it is now proposed that the “too hot” signal 314 be takenoff, as indicated at 318, to be provided to one of the terminal pins 212(FIG. 2). From that terminal pin 212, the “too hot” signal may beprovided to an external device (discussed below, not shown in FIGS. 2and 3) in order to control an external cooling device dedicated to thedocking location at which the DUT is being burned in.

In one embodiment, the “catastrophic” signal 316 may be applied ininverted form to the AND gate 306, so that the AND gate 306 passes theclock signal selected by the multiplexer 304 when the “catastrophic”signal 316 is “0” (not asserted). When the “catastrophic” signal 316 is“1” (asserted), the AND gate blocks off the clock signal from the corelogic and essentially places the DUT in an inactive mode. With no gatetoggling occurring, the DUT may then cool off more rapidly than when thelower frequency clock signal is applied to the core logic. As the DUTcools to a temperature below the pre-programmed “catastrophic” setpoint, the thermal sensor 310 switches the signal 316 to “0” to allowthe AND gate 306 to pass the clock signal output from the multiplexer304. The DUT therefore again runs using that clock signal. Thus theoutput of the AND gate 306 is equivalent to an internal temperaturesensitive variable speed clock signal for the core logic.

It is possible that even with the clock signal gated off from the corelogic, power dissipation due to leakage currents may be sufficient toprevent the DUT from cooling from the “catastrophic” temperature level.Consequently, it is now further proposed that the “catastrophic” signal316 also be taken off, as indicated at 320, to be provided to one of theterminal pins 212 (FIG. 2). From that terminal pin, the “catastrophic”signal may be provided to an external device (discussed below, not shownin FIGS. 2 and 3) in order to switch off the power supply for thedocking location at which the DUT is being burned in. With thisarrangement, there may be theoretically no limit to the powerdissipation level of DUTs for which the docking location could stillfunction successfully.

From the foregoing, it will be understood that the thermal sensingcircuit operates to monitor the internal temperature of the DUT.Moreover, one of terminal pins 212 coupled to the thermal sensingcircuit provides a signal external to the DUT to indicate whether theinternal DUT temperature exceeds a threshold temperature thatcorresponds to the target burn-in temperature set point. Another one ofthe terminal pins 212, also coupled to the thermal sensing circuit,provides another signal external to the DUT to indicate whether theinternal DUT temperature exceeds another threshold temperature thatcorresponds to the “catastrophic” temperature set point.

It will also be appreciated that the DUT may incorporate othercircuitry, which is not shown, to disable blocks 202, 204, 208 when theDUT is not undergoing self-heating burn-in and to supply another clocksignal, suitable for normal operation of the DUT, to the core logic 206.

FIG. 4 is a perspective view of a typical one of the burn-in boards 106,as provided according to some embodiments. As seen from FIG. 4, theburn-in board 106 includes a board substrate 402 on which one and onlyone socket 404 is mounted. The socket 404 is suitable for receiving andholding a DUT and interfacing the DUT to other components on the burn-inboard 106. The substrate 402 may be installed on a metal frame 406 thatis also part of the burn-in board 106. The metal frame may havelaterally facing holes 408 (only two visible in FIG. 4) on both sides ofthe frame to facilitate secure handling of the burn-in board by therobotic arm 104 of the system 100.

The burn-in board may also include an edge connector 410 which runsalong one edge of the burn-in board. The edge connector may allow forcoupling of signals (as well as power and ground) between the burn-inboard and a connector (not separately shown) on one of the dockinglocations. In addition, other components of the burn-in board 106 arepresent in a region 412 shown in FIG. 4.

FIG. 5 is a block diagram representation of the burn-in board 106 shownin FIG. 4. Shown in FIG. 5 are the substrate 402, socket 404 and edgeconnector 410. Other components of the burn-in board 106 include LEDs(light emitting diodes) 502, biasing resistors 504 and de-couplingcapacitors 506.

The LEDs 502 may include a green LED which blinks when the burn-inprocedure is proceeding normally for a DUT (not shown in FIG. 5) held inthe socket 404, a yellow LED that is turned on during operation of a fan(discussed below) at the docking location to which the burn-in board isdocked, and a red LED that is turned on when the DUT is outputting the“catastrophic” signal described above.

FIG. 6 is a schematic side cross-sectional view of a column of dockinglocations 602 mounted on a typical one of the support structures 102(FIG. 1) of the system 100. (Although four docking locations 602 areshown in FIG. 6, it will be understood that columns of docking locationson the support structures may include more or fewer than four dockinglocations.)

A respective burn-in board 106 is shown docked to each of the dockinglocations 602 on a front side 604 of the support structure 102. Thesocket 404 of each burn-in board 106 is also shown, and it is to beunderstood that a respective DUT (not separately shown) is held in eachsocket 404.

Each docking location 602 includes a respective support member 606 onwhich the respective burn-in board 106 is supported. The support member606 may extend horizontally from the front side 604 of the supportstructure 102. The support member may include roller bearings (notseparately shown) or the like to facilitate docking of the burn-in boardto the docking location 602.

In addition, each docking location 602 includes a connector (notseparately shown) to couple to the edge connector 410 (FIGS. 4 and 5;not separately shown in FIG. 6) of the burn-in board 106 docked to thedocking location.

Further, each docking location 602 includes a driver circuit 608 mountedon the rear side 610 of the support structure 610 positioned oppositethe burn-in board docked to the corresponding docking location 602.Aspects of the driver circuit 608 will be described below. The drivercircuit is coupled to the burn-in board to exchange signals with theburn-in board and to provide power to the burn-in board.

Still further, each docking location 602 may include a fan 612 toselectively provide a stream of air (represented by dashed arrow 614) toselectively cool the DUT (not separately shown) installed on the burn-inboard 106 docked at the docking location. In some embodiments, each fan612 may be a so-called “squirrel cage” variable speed fan such as thePanasonic model FAL5F12LH 12 volt brushless fan available fromMatsushita. Each fan 612 may be controlled by a respective PWM (pulsewidth modulation) control signal schematically indicated at 616 andprovided by the respective driver circuit 108 of the docking location602 to which the fan 612 belongs. In some embodiments the fan controlsignal 616 is generated by the respective driver circuit 608 at leastpartially in response to the “too hot” signal 318 (FIG. 3) output fromthe DUT (not separately shown) installed in the burn-in board 106 dockedto the docking location of which the respective fan 612 is a part. Eachfan may, for example, be capable of generating an air flow on the orderof about ten cubic feet per minute.

Each docking location 602 may further include a duct to direct the airstream 614 from its fan 612 to the DUT being burned in at the dockinglocation. In some embodiments, at least some of the ducts may each beintegrated with (formed in) the support member 606 that is part of thedocking location that is immediately above the docking location inquestion. That is, at least some of the support members 606 may be atleast partially hollow to form a respective duct to direct air from arespective fan 612 to a respective socket 404 to cool a DUT (notseparately shown) installed in the socket. Assuming that the fan 612supplies an air flow of ten cubic feet per minute, the duct may have anoutlet sized to provide an airflow of about 640 linear feet per minute(or 1200 LFM in other embodiments).

In some embodiments, the fan 612 may be turned on and off by the drivercircuit 608 in response to the DUT in question asserting or de-assertingthe “too hot” signal. In other embodiments, the fan provides at least atickle of air throughout burn-in and the volume of air provided by thefan is selectively ramped up (i.e., the fan speed is selectively rampedup) in response to periods of time in which the DUT asserts the “toohot” signal. In some embodiments, the air stream provided by the fan atmaximum speed may be sufficient to dissipate up to 85 watts of power.

In some embodiments, another type or types of cooling device may beincluded in each docking location in addition to or instead of the fans.The other type or types of cooling device may include a device whichcirculates a liquid coolant to cool the DUT, a thin film thermoelectriccooling device and/or a Peltier plate. In each case the amount ofcooling provided by the cooling device or devices may be controlled inresponse to the “too hot” signal output from the DUT.

FIG. 7 is a block diagram representation of a typical one of the drivercircuits 608 shown in FIG. 6. The driver circuit 608 may include a boardsubstrate 702. In its physical embodiment the board substrate may havesimilar dimensions to the board substrate of the burn-in board, sayabout four inches by six inches. The other components of the drivercircuit 608, enumerated below, may all be mounted on the board substrate702.

The driver circuit 608 may include a control circuit 704, one or morecommunication interfaces 706, a DUT power supply 708, a fan drivecircuit 710 and a clock signal generator 712. The communicationinterface(s) 706 are coupled to the control circuit 704 to allow thecontrol circuit 704 to exchange communications with other components ofthe system 100. The DUT power supply 708 and the fan drive circuit 710are coupled to the control circuit 704 to be controlled by the controlcircuit 704.

The DUT power supply may include a MOSFET (metal oxide semiconductorfield effect transistor) to control the supplying of power to theburn-in board 106 and hence to the DUT that is being burned in at thedocking location of which the driver circuit is a part. The controlcircuit 704 may turn off the DUT power supply 708 in response toreceiving the “catastrophic” signal from the DUT.

The fan drive circuit 710 selectively provides a drive signal to the fan612 (FIG. 6) to control the fan in response to the “too hot” signalprovided from the DUT to the driver circuit 608. The control circuit 704may be arranged to detect failure of the associated fan by monitoringthe power drawn (or failure to draw power) by the fan. If necessary thecontrol circuit may signal to the system controller (described below) toindicate failure of the fan.

The clock signal generator 712 may provide the two phase-shifted clocksignals for the clock generation and selection block 204 (FIGS. 2 and 3)of the DUT. These clock signals are coupled to the DUT via the burn-inboard 106. (In some embodiments, the clock signal generator may beprovided on the burn-in board rather than as part of the drivercircuit.)

The control circuit 704 may, in some embodiments, be implemented as aPLD (programmable logic device). In addition to controlling the DUTpower supply 708 and the fan drive circuit 710 in response to signalsoutput from the DUT, the control circuit 704 may perform the function ofgenerating suitable signals to initialize the state machine 208 (FIG. 2)of the DUT so that the DUT is exercised as required during the burn-inprocedure. The control circuit 704 may also detect whether the burn-inprocedure properly commences upon triggering the state machine. Ineffect, in this way the control circuit may also detect whether thedocking of the burn-in board to the docking location was successful andwhether the DUT is properly installed in the burn-in board socket. Ifeither of these is not the case, the burn-in board will not properlydraw power from the power supply 708, which may be detected by thecontrol circuit 704.

The control circuit 704 may also monitor results of the burn-inprocedure. For example, the control circuit 704 may detect whether theDUT successfully completes the burn-in procedure or fails during theburn-in procedure. In addition, the control circuit 704 may communicatewith a system controller (to be discussed below) to report events orconditions such as failure to commence burn-in properly, failure of theDUT during burn-in, or shutting off of power to the DUT in response tothe “catastrophic” signal from the DUT.

FIG. 8 is a block diagram showing a controller 802 and other controlaspects and components of the system 100. Thus the controller 802 alsoconstitutes part of the system 100, and may be constituted, for example,by a suitably programmed personal computer. The controller 802 may be indata communication with the driver circuits 608 at all of the dockinglocations to receive reports from the driver circuits of the eventsdescribed in the previous paragraph and to track and control theduration of the burn-in procedures at all of the docking locations. Thecontroller 802 may also be coupled to the robotic arm 104 (also shown inFIG. 1) so as to control the robotic arm so that it transports andmanipulates DUTs, burn-in boards and/or trays in a manner to bedescribed below. In some embodiments, if a second robot 804 is alsoincluded in the system to, e.g., divide tasks with the robotic arm 104(as in an embodiment illustrated in FIG. 11), the controller 802 may becoupled as well to the second robot 804 to control operation thereof.

In some embodiments, the state of the “catastrophic” signal is passedfrom each driver circuit to the controller 802, and the controller 802,rather than the driver circuit, determines whether and when to shut offthe power for the corresponding burn-in board and when to turn the powerback on. The controller 802 may make this determination after samplingthe “catastrophic” signal and determining that it has remained on formore than a pre-determined period of time.

FIG. 9 is a perspective view of a robot end effector 902 which iscoupled to the end of the robotic arm 104 in accordance with someembodiments. In some embodiments, the end effector 902 is capable offour different functions, namely (1) handling DUTs, (2) handling burn-inboards, (3) handling trays and (4) detecting conditions in the system100.

The end effector 902 may include a wrist portion 904 by which the endeffector 902 may be connected to the robotic arm 104. In addition theend effector includes a first pair of opposed fingers 906 coupled to thewrist portion 904. These fingers may be pneumatic gripper fingers. Afunction of the fingers 906 is to engage burn-in boards so that therobotic arm may transport the burn-in boards. Each finger 906 may havean inwardly pointing pair of pins 908 to engage the holes 408 (FIG. 4)in the metal frame 406 of a burn-in board. (Only one of the two pairs ofpins is visible in FIG. 9.) A distance between the fingers 906 maysubstantially correspond to a width of the burn-in boards to betransported by the robotic arm 104.

Continuing to refer to FIG. 9, the end effector may also include secondfingers 910 each of which is coupled to an end of a respective one ofthe first fingers 906. Thus the second fingers 910 are coupled to thewrist portion 904 via the first fingers 906. The second fingers 910 maybe suitably configured for engaging trays and transporting trays betweentray holders 110 (FIG. 1), and also may be pneumatic gripper fingers.The second fingers 910 may have a length dimension that is perpendicularto the length dimension of the first fingers 906. The second fingers 910may define a gap therebetween which is wider than the gap between thefirst fingers 906. The second fingers 910 may be offset slightly so asnot to interfere with the vacuum head 912, which will now be discussed.

The vacuum head 912 may be coupled to the wrist portion 904 of the endeffector 902 via one of the fingers 906. In particular, the vacuum head912 may be mounted on an outer side 914 of the finger 906. A function ofthe vacuum head 912 is to engage DUTs to be transported by the roboticarm 104. The vacuum head 912 may be composed of a number of individualvacuum cups 916 arrayed so as to define a plane. For example, the vacuumhead may include four vacuum cups (of which only three are visible inthe drawing). In some embodiments, the vacuum for the vacuum head 912 isgenerated locally with air pressure, using the Bernoulli principle,rather than relying on a connection to a central source of vacuum.

In some embodiments, the end effector 902 may also include a laserdistance detector 918 coupled to the wrist portion 904 of the endeffector 902 via one of the fingers 906 and/or 910. The laser distancedetector 918 may be employed by the system 100 to detect whether aburn-in board is present at a particular docking location, whether a DUTis installed in a particular burn-in board, whether a DUT is present ona tray, whether a tray is present in a tray holder, and/or to detectother conditions in the system 100. Having a laser distance detector 918on the end effector 902 may be particularly helpful in enabling thesystem 100 to re-initialize in the event of a power outage, softwaredisruption, etc.

In some embodiments, the robotic arm 104 may be a six-axis robotic arm,such as the model no. VS-6577-E available from Denso Robotics, LongBeach, Calif. In other embodiments, a “linear bearing” or “XYZ” type ofrobot may be used in place of the robotic arm referred to above.

The installation station 108 (FIG. 1) may operate in accordance withconventional principles to perform de-installation of a DUT from aburn-in board or installation of a DUT in a burn-in board. Morespecifically, the installation station 108, whether actuated by therobotic arm 104 or under its own power, may operate to open a socket ona burn-in board presented to the installation station so that a DUT maybe removed from the socket. With the old DUT having been removed, a newDUT may thereafter be installed in the socket at the installationstation. (Although not indicated in FIG. 8, the installation station maybe controlled by the controller 802, and for that purpose may be coupledto the controller 802 by a signal path which is not shown.)

FIG. 10 is a flow chart that illustrates a process for performing aburn-in procedure in the system 100 in accordance with some embodiments.Initially, as indicated at 1002, and if necessary at this stage ofoperation of the system 100, the controller 802 (FIG. 8) may control therobotic arm 104 to move one or more trays from one of the tray holders110 (FIG. 1) to another of the tray holders. Then, assuming that aburn-in procedure has been completed for a DUT 112 installed in aburn-in board 106 (referred to by the acronym “BIB” in FIG. 10) at oneof the docking locations 602, the controller 802 causes the drivercircuit 608 at the docking location to cut off power to the DUT, asindicated at 1004 in FIG. 10. The controller then controls the roboticarm 104 to remove the burn-in board 106 from the docking location inquestion and transport the burn-in board to the installation station108, as indicated at 1004. To explain this stage of the process in moredetail, the controller controls the robotic arm 104 to position the endeffector 902 at the docking location in question (unless the endeffector was pre-positioned at the docking location in anticipation ofthe completion of the burn-in going on at the docking location). Thenthe robotic arm causes the fingers 906 (FIG. 9) to engage the burn-inboard and to de-couple the burn-in board from the docking location. Oncethis has been done, the end effector is moved with the burn-in boardengaged therein to present the burn-in board to the installation station108, as indicated at 1006 in FIG. 10.

At this point, as indicated at 1008, the installation station 108 andthe end effector 902 are operated to de-install the processed DUT fromthe burn-in board. Then, with the burn-in board remaining at theinstallation station 108, the robotic arm operates, as indicated at1010, to transport the processed DUT to a tray located in theappropriate one of the tray holders 110. Next, the robotic arm operates,as indicated at 1012, to engage a new (to-be-processed) DUT in a tray atanother one of the tray holders 110 and to transport the new DUT to theinstallation station 108. The installation station 108 is then operatedto install the new DUT in the burn-in board, as indicated at 1014.

The robotic arm now operates, as indicated at 1016, to transport theburn-in board with the new DUT to the docking location from which theburn-in board was previously removed, and the robotic arm furtheroperates to dock the burn-in board to the docking location. The drivercircuit 608 (FIG. 6) then, as indicated at 1018, turns on the powersupply for the burn-in board (and thus also for the new DUT installed onthe burn-in board) in order to start the burn-in procedure for the newDUT. The self-heating burn-in procedure for the new DUT then proceeds,as indicated at 1020. As indicated at decision block 1022, theself-heating burn-in procedure continues until completed (or until theDUT fails), and the process then loops back to 1002 (if required) and1004.

During the self-heating burn-in procedure, the driver circuit 606 (FIGS.6 and 7) provides a suitable signal to the DUT to actuate the statemachine 208 (FIG. 2) of the DUT, so that the state machine appliespatterns to the core logic 206 to exercise the DUT during the burn-inprocedure. The clock generation and selection block 204 (FIGS. 2 and 3)of the DUT initially provides the higher (e.g., 20 MHz) clock signal tothe core logic 206 to rapidly toggle the gates of the DUT so that theDUT is rapidly raised to the target burn-in temperature. In someembodiments, the target temperature may be reached in, e.g., 15 secondsfor a DUT that does not include a heat sink, or in about two to threeminutes for a DUT that includes a heat sink. Once the target temperatureis reached, the clock generation and selection block 204 may respond tothe “too hot” signal 314 (FIG. 3) provided by the thermal sensingcircuit 202 by alternating between providing the higher clock signal andproviding a lower clock signal (e.g., 10 MHz) to the core logic to aidin maintaining the internal DUT temperature at the target. In addition,the driver circuit 608 (FIG. 6) also receives the “too hot” signal, andresponds to the “too hot” signal by controlling the fan 612 to aid incooling the DUT to maintain the DUT at the target temperature.

It is expected that the fan 612 and the lower clock signal willcustomarily keep the DUT at the target temperature. However, in theevent of a “catastrophic” rise in temperature to, e.g., 10 or 12 degreesabove the target temperature, the “catastrophic” signal 316 (FIG. 3) isasserted by the thermal sensing circuit 202 and is taken off at 320 tobe provided to the driver circuit 608 (FIGS. 6 and 7). The assertion ofthe “catastrophic” signal immediately causes the clock signal from themultiplexer 304 (FIG. 3) to be gated off at the AND gate 306. Moreover,the driver circuit 608 responds to the “catastrophic” signal withinabout one second by cutting off the power for the DUT. The drivercircuit 608 keeps the power off for a predetermined period (say aboutten seconds) and then restores the power. When a cut-off of power occursin response to the “catastrophic” signal, the driver circuit so informsthe controller 802 (FIG. 8) of the system so that the controller 802 canadd the power down time to the required burn-in period to insure thatthe full burn-in is applied to the DUT. (In other embodiments, as notedabove, the controller 802 controls removal of power to the DUT inresponse to the “catastrophic” signal.)

Another event that is provided for, although not expected normally tooccur, is a failure to properly install the DUT in the burn-in board. Todeal with this possibility, the driver circuit 608 (FIGS. 6 and 7) maydetermine, when the burn-in board is powered up at 1018 (FIG. 10),whether the DUT properly begins to draw power and/or begins to functionproperly for burn-in, as may be indicated by a signal output from theDUT to the driver circuit. If not, faulty installation of the DUT in thesocket is a possible cause, and accordingly the driver circuit mayrespond to the failure of the DUT to draw power or to begin functioningproperly by signaling to the controller 802 to cause the controller tocontrol the robotic arm so that the burn-in board is returned to theinstallation station 108 (FIG. 1) to reinstall the new DUT in the socketof the burn-in board.

The process of FIG. 10 is performed with respect to a single burn-inboard associated with (customarily docked to) a single one of thedocking locations of the system, and is performed more or lesscontinuously. Thus the process of FIG. 10 results in a potentiallyendless sequence of DUTs being burned in at the docking location inquestion. It will be understood that essentially the same process may besimultaneously performed by the system 100 with respect to each one ofthe other docking locations of the system (e.g., dozens or hundreds ofdocking locations). Consequently, for example, dozens or hundreds ofDUTs may at any one time be undergoing the burn-in procedure, each at arespective one of the docking locations. Also, at any given time, one ofthe burn-in boards may be undergoing the process of removal from itsassociated docking location, replacement of a processed DUT with a newDUT, and return of the burn-in board to the docking location, asindicated at 1006 to 1016 in FIG. 10. The number of docking locationsand burn-in boards, and the duration of the burn-in period, may be suchas to occupy the robotic arm substantially continuously with servicingthe various docking locations. The servicing of the docking locations,and the performance of burn-in procedures at each docking location, areasynchronous, in that the timing at which a burn-in board is cycled toand from a docking location and the timing at which a burn-in procedureis performed at the docking location are independent of the timing ofservicing and performing burn-in at any other docking location.

The system described with reference to FIGS. 1-10 may result in costsavings in a number of different ways. For example, capital costsincurred for sockets and burn-in boards may be substantially decreased,since the system of FIGS. 1-10 promotes very high (almost constant)utilization of burn-in boards and sockets. Moreover, wear on the burn-inboard sockets may be reduced since a socket is opened only once for eachexchange of a processed DUT for a new DUT. Also, when a single-socketburn-in board as described above needs to be scrapped because the sockethas broken, it costs much less to replace the burn-in board than itwould cost to replace a conventional 15-socket burn-in board because oneof the 15 sockets has broken. Further, expensive facilities such asburn-in ovens and BLUs (burn-in loader/unloaders) can be dispensed with.Since these facilities are not needed, floor space requirements are alsoreduced, leading to further savings in capital costs.

Savings in labor costs may also be realized, since the burn-in processillustrated above only requires the operator to place stacks of trayswith new DUTs in one tray holder and to remove trays of processed DUTsafter a lapse of time during which processing occurs. This may eliminateseveral hand labor steps required either for conventional oven burn-inor for a self-heating burn-in process as proposed in theabove-referenced related patent application.

The quality of the burn-in process may also be improved in the system ofFIGS. 1-10. Since each docking location has facilities for individuallycooling the DUT being burned in at the docking location, the actualburn-in temperature may be regulated to match the target temperature.Even in the case of variations in DUTs that involve high powerdissipation by some of the DUTs, the capacity to interrupt the powersupply if necessary on an individual basis allows the system to processall DUTs successfully, while tracking actual burn-in time to assure thatthe specified burn-in period is applied to each DUT.

Because of the relatively small amount of floor space required for thesystem of FIGS. 1-10, it may be feasible to integrate the burn-inprocess in the same factory floor area used for other testing process,rather than transporting the lots of DUTs to another area or buildingfor burn-in, as is commonly done with conventional oven burn-in.Integration of burn-in facilities with other test locations may lead toadditional improvements in throughput. Also, the burn-in processdescribed herein may require less power than conventional oven burn-inprocesses.

The controller 802 referred to above may be programmed to track each andevery DUT handled by the system, and to sort DUTs of different lots tothe respective output trays for the lots. Consequently, more than onelot of DUTs may be processed in the system at a given time. The mixingof lots within the burn-in facility may lead to improved efficiency,less waiting time, and improved throughput.

The increased efficiency exhibited by the system of FIGS. 1-10 may makeit feasible both to increase the proportion of each lot subjected toburn-in testing (to, e.g., 100% burn-in) and to decrease the duration ofburn-in (to, e.g., 6 to 10 minutes).

The system of FIGS. 1-10 may also allow for more rapid and lessexpensive debugging and manufacturing processes for the burn-in boards.

If the burn-in time per DUT is decreased, as suggested above, the timerequired by the robotic arm to service each docking location may becomea limiting factor on the throughput provided by the system. To addressthis issue, a modified system is proposed in accordance with embodimentsdescribed below in connection with FIGS. 11-20. Before describing thesystem of FIGS. 11-20 in detail, differences relative to the system ofFIGS. 1-10 will be summarized:

(A) Installation station eliminated;

(B) Burn-in boards permanently docked to support structures;

(C) Robotic arm equipped to open sockets/install DUTs in burn-in boardsat the support structures;

(D) Robotic arm equipped to transport and install multiple DUTs (e.g.,six DUTs) at one time;

(E) Support structures oriented radially rather than tangentiallyrelative to the robotic arm;

(F) Robotic arm equipped to hold one group of DUTs while de-installingor installing another group of DUTs;

(G) Additional robot provided to stage DUTs between tray holders andstaging tray from/to which first robot transports DUTs.

FIG. 11 is a schematic plan view of a system 1100 provided according tosome embodiments to perform self-heating burn-in of DUTs. As notedabove, the system shown in FIG. 11 is somewhat different in somerespects from the system 100 of FIGS. 1-10.

The system 1100 includes a plurality of vertical support structures 1102arranged at various radial positions around a robotic arm 1104 which isalso part of the system 1100. Unlike the support structures 102 of thesystem 100 (FIG. 1), the support structures 1102 of the system 1100 areoriented radially so that the front sides of the support structures 1102face tangentially rather than radially inwardly toward the robotic arm1104. Each support structure 1102 may have mounted thereon several tiersof burn-in stations, with only one tier 1106 of burn-in stations beingvisible in FIG. 111 for each support structure 1102. Each burn-instation is represented by a respective burn-in socket 1108 shown in FIG.11. Each socket 1108 may, like the socket 404 described with referenceto FIGS. 4 and 5, be provided to receive and hold a DUT to be burned-inat the corresponding burn-in station. As used herein and in the appendedclaims, “burn-in station” refers to a location at which a socket ispresent to hold a DUT in situ for a burn-in procedure.

The system 1100 may also include a tray holder 1110-1 for holding traysof DUTs to be processed in the system, a tray holder 1110-2 for holdingDUTs that were burned in successfully, a tray holder 1110-3 for holdingDUTs that failed during burn-in, and a tray holder 1110-4 for holdingempty trays. As will be understood from the discussion of tray holders110 (FIG. 1) of system 100 and from other aspects of system 100, thenumber of tray holders included in system 1100 may be augmented if it isdesired to process more than one lot of DUTs in the system 1100 at anygiven time.

The system 1100 may further include a staging tray 1112 that holds agroup of (e.g., six) DUTs to be transported by the robotic arm 1104 to atier 1106 of burn-in stations, and a group of (e.g., six) DUTs that havebeen processed at one of the tiers 1106 and have been transported fromthe tier to the staging tray. In addition, the system 1100 may include asecond robotic arm 1114 to transport DUTs (individually and/or ingroups) between the staging tray 1112 and the tray holders 1110-1,1110-2 and 1110-3.

The robotic arm 1104 may, like the robotic arm 104 of system 100, be aso-called six-axis robotic arm. However, the robotic arm 1104 may havean end effector (examples shown in FIGS. 14-17 and 19 and discussedbelow) that is substantially different from the end effector 902(illustrated in FIG. 9) which is part of the robotic arm 104 and whichwas described above. The second robotic arm 1114 may, in someembodiments, be a SCARA (selectively compliant articulated robot arm) orfour-axis robot, such as the model HS-E 5 kg series available from DensoRobotics.

FIG. 12 is a partial isometric view of one of the tiers 1106 of burn-instations mounted on a front side 1202 of one of the support structures1102. Each burn in station is indicated by a reference numeral 1204 andincludes a respective burn-in board 1206. Each burn-in board 1206 mayinclude a single one of the sockets 1108, and may otherwise resemble theburn-in board 106 illustrated in FIGS. 4 and 5, except that the burn-inboard 1206 need not have an edge connector, since the burn-in boards1206 may be permanently installed at the burn-in stations 1204 and mayeach be connected to a respective driver circuit (not shown in FIG. 12)via cables or strap connectors 1208 which extend through apertures 1210in the support structure 1102 to the driver circuits.

In some embodiments, two or more of the single-socket burn-in boards1206 may be replaced by a burn-in board that includes more than onesocket. For example, FIG. 13 shows, somewhat schematically, a burn-inboard 1302 that has six sockets 1108. Thus the burn-in board 1302 maycorrespond to an entire tier 1106 of burn-in stations, each of which maycorrespond to one of the sockets 1108. As seen from FIG. 13, each of theburn-in boards 1302 may be permanently installed on the front side 1202of a support structure 1102. Although only three tiers 1106 are shown inFIG. 13, in some embodiments each of the support structures 1102 mayhave more than three (e.g., seven) tiers of burn-in stations mountedthereon. It should also be understood that each burn-in station may alsoinclude the same or substantially the same driver circuit, fan and ductas were described in connection with the docking locations 602 (FIG. 6)of the system 100, although some of these components are not expresslyshown in the drawings for the system 1100. Moreover, the DUTs to beburned-in in the sockets 1108 of the system 1100 may be the same asthose described above in connection with FIGS. 2 and 3.

FIG. 14 is a schematic isometric view of a robot end effector 1402 thatmay be mounted on the robotic arm 104 used in the system 1100. The endeffector 1402 includes a wrist portion (schematically indicated at 1404)by which the end effector 1402 may be connected to the robotic arm 1104(FIG. 11, not shown in FIG. 14). The end effector 1402 also includes asocket-opening member 1406 which is mounted on the wrist portion 1404.The socket-opening member 1406 is configured to simultaneously pressdown on all (e.g., six) sockets 1108 (FIG. 12 or FIG. 13, not shown inFIG. 14) of a tier 1106 of burn-in stations 1204 to simultaneously openall of the sockets 1108. As expressed with a colloquial term used bythose who are skilled in the art, the socket-opening member 1406 isconfigured to simultaneously “stomp” all of the sockets 1108 of a tier1106.

The end effector 1402 further includes a shaft 1408 mounted on the wristportion 1404 and extending parallel to the socket-opening member 1406.In addition, the end effector 1402 includes a first linear array 1410 ofvacuum heads mounted along the shaft 1408 and a second linear array 1412of vacuum heads mounted along the shaft 1408. For example, each of thearrays 1410, 1412 may include six vacuum heads to simultaneously holdand transport six DUTs. As seen from FIG. 14, there may be a 180°difference in orientation between the arrays 1410, 1412. That is, whenthe array 1410 is facing directly upward, the array 1412 may facedirectly downward. As best seen from FIG. 17, the shaft 1408 may bemounted to the wrist 1404 in such a manner as to allow the shaft 1408 tobe rotated about its longitudinal axis, thereby allowing the orientationof the two arrays 1410 and 1412 to be shifted between an upwardorientation and a downward orientation.

Each vacuum bead may include four vacuum cups. As in the case of the endeffector 902 described above, in some embodiments the vacuum for thevacuum heads of the arrays 1410, 1412 may be generated locally with airpressure, using the Bernoulli principle, rather than by a connection toa central source of vacuum.

In some embodiments, illustrated in FIG. 15, the socket-opening member1406 and the shaft 1408 may be aligned with the wrist portion 1404, andmay be mounted to the wrist portion 1404 by respective ends of themember 1406 and of the shaft 1408. In other embodiments (illustrated inFIG. 16), if necessary or desirable to reduce the moment of inertia ofthe end effector 1402, the socket-opening member 1406 and the shaft 1408may be angled relative to the wrist portion 1404, and may be mounted tothe wrist portion 1404 at a central location along the member 1406 andthe shaft 1408.

FIG. 17 is a schematic side view of the robot end effector 1402 as itinteracts with one of the burn-in stations 1204, and particularly with asocket 1108 of the burn-in station 1204 (both shown in phantom).

As suggested by prior discussion, the end effector 1402 includes amechanism (e.g., a 180° pneumatic rotor) schematically indicated at 1702to rotate the shaft 1408 about its longitudinal axis to change theorientation of the vacuum head arrays 1410, 1412 from upward-facing todownward-facing, and vice versa. Also included in the end effector 1402is a mechanism schematically indicated at 1704 to raise and lower theshaft 1408 so that a DUT (not shown) held by a vacuum head of one of thearrays 1410, 1412 may be presented to or removed from the socket 1108.In addition, the end effector 1402 includes a mechanism schematicallyindicated at 1706 to raise and lower the socket-opening member 1406 toactuate “stomping” of the socket 1108.

A tooling ball 1708 may be provided on the end effector 1402 to aid inaligning the end effector 1402 with the burn-in station 1204. Forexample, the tooling ball may interact with a feature such as a grooveor indentation (not separately shown) on the burn-in station.

The end effector 1402 may also include a finger 1710 mounted on thesocket-opening member 1406. The finger 1710 has a tip 1712 that extendsforwardly of the socket-opening member 1406. The finger 1710 may beprovided, as described below in connection with FIG. 19, to push apivotable nozzle portion (not shown in FIG. 17) of an air duct (notshown in FIG. 17) for the burn-in station 1204.

FIG. 18 is a schematic plan view of the staging tray 1112 (seen in FIG.11 as part of the system 100). Referring to FIG. 18, the staging tray1112 may include, for example, a 2×6 array of compartments 1802, each ofwhich is configured to hold a respective DUT (only one DUT 112 shown inthe drawing). A mechanism 1804 that is shown in phantom may be includedin the staging tray 1112 to adapt the sizes of the compartments to matchthe size of the DUTs to be held in the staging tray 1112. One row of thecompartments 1802 may, at times, hold DUTs staged at the tray 112 on theway from the tray holder 1110-1 (FIG. 11) to a tier of burn-in stations.The other row of compartments 1802 may, at times, hold DUTs staged atthe tray 1112 on the way from a tier of burn-in stations to the trayholder 1110-2 or the tray holder 1110-3 (FIG. 11), as the case may be.The robotic arm 1114 may operate to transport DUTs between the stagingtray 1112 and the tray holders 1110-1, 1110-2, 1110-3. The robotic arm1104 may operate to transport DUTs, in groups of six for example,between the staging tray 1112 and the burn-in stations on the supportstructures 1102. In one visit by the robotic arm 1104 to the stagingtray 1112, one array of vacuum heads of the robotic arm 1104 maysimultaneously deposit six processed DUTs in a row of the compartments1802, and immediately before or after so doing, the other array ofvacuum heads may simultaneously pick up six to-be-processed DUTs fromthe other row of the compartments 1802. (In the event that picking upthe to-be processed DUTs follows the depositing of the processed DUTs,the same array of vacuum heads may be used for both operations.)

To assure interoperability of the end effector 1402 with the tiers 1106of burn-in stations 1204 and with the staging tray 1112, it may bedesirable to have the linear spacing of the vacuum heads of the endeffector match the linear spacing of the sockets 1108 of the tiers 1106.Also, it may be desirable for the linear spacing of the compartments1802 of the staging tray 1112 to match the linear spacing of the vacuumheads of the end effector 1402.

FIG. 19 is a schematic side view showing the end effector 1402 (portionsof end effector omitted to simplify the drawing) interacting with aburn-in station 1204 of the system 1100. FIG. 19 shows aspects of someembodiments of the burn-in station that are omitted from other drawings.

As in the embodiment of FIG. 6, each burn-in station includes a duct1902 to direct a flow of air (represented by arrow 1904) from a fan (notshown) mounted on the rear side 1906 of the support structure 1102toward the socket 1108 of the burn-in station. As before, each duct maybe integrated in a support member (also indicated by reference numeral1902) which supports the burn-in board (not separately shown) of theburn-in station. Each duct/support member 1902 may include a nozzle1908, to complete the airflow path. The nozzle 1908 may be pivotablebetween a first position (indicated at 1910) in which the nozzle 1908points downwardly toward the socket 1108 of the burn-in station and asecond position (indicated at 1912) in which the nozzle 1908 isdeflected toward the support structure 1102 to accommodate the endeffector accessing the socket. The nozzle 1908 may be deflected by beingpushed by the finger 1710 (FIG. 17, not shown in FIG. 19) of the endeffector 1402. There may be associated with each nozzle 1908 a spring orother bias device (schematically indicated at 1914) to bias the nozzlefrom the second position to the first position.

The control architecture illustrated in FIG. 8 is also applicable to thesystem 1100 illustrated in FIGS. 11-19. That is, the system 1100 mayalso include a controller 802 (FIG. 8), such as a suitably programmedpersonal computer that is in communication with and controls roboticarms 1104, 1114 (FIG. 11, indicated as robots 104, 804 in FIG. 8). Thecontroller may also be in communication with driver circuits at theburn-in stations of the system 1100.

FIG. 20 is a flow chart that illustrates a process for performing aburn-in procedure in the system 1100. Initially, as indicated at 2002,the controller 802 (FIG. 8) may control the robotic arm 1114 (FIG. 11)to transport processed DUTs from the staging tray 1112 to the trayholder 1110-2 or 1110-3, as the case may be, and to transportto-be-processed DUTs from tray holder 1110-1 to the staging tray 1112.(Staging of DUTs between the tray holders and the staging tray mayoverlap in time with the robotic arm 1104 servicing a tier of burn-instations, as described below) Then, as indicated at 2004, the controller802 controls the robotic arm 1104 to use one of its arrays of vacuumheads to simultaneously pick up a group of new (to-be-processed) DUTsfrom a row of compartments of the staging tray 1112 and to transport thegroup of new DUTs to a tier of burn-in stations at which there are DUTsfor which a burn-in procedure has just been completed.

With the new DUTs present at the tier of burn-in stations, thecontroller 802 causes the robotic arm 1104 to use its socket-openingmember 1406 (FIG. 14) to simultaneously open all of the sockets of thetier of burn-in stations, as indicated at 2006 in FIG. 20. With the newDUTs held by one of the arrays 1410, 1412 of vacuum heads in proximityto the sockets, the robotic arm 1104, under control of the controller,uses the other one of the arrays of vacuum heads to de-install (2008,FIG. 20) the respective processed DUTs from each of the sockets of thetier of burn-in stations. Then, as indicated at 2010, with the processedDUTs held in proximity to the sockets by one of the arrays of vacuumheads, the robotic arm 1104 uses the other of the arrays to install thenew DUTs in the sockets of the tier of burn-in stations. Thus, all ofthe processed DUTs are removed simultaneously from the sockets of thetier of burn-in stations, then shortly thereafter, all of the new DUTsare installed simultaneously in the sockets of the tier of burn-instations.

Next, as indicated at 2012, the driver circuits for the tier of burn-instations turn on the power supplies for the burn-in boards at theburn-in stations to start the burn-in procedure for the new DUTsinstalled in the sockets of the tier of burn-in stations. While theburn-in procedure starts and continues, the robotic arm 1104 transports(2014, FIG. 20) the group of processed DUTs just removed from the tierof burn-in stations to the staging tray. In the same visit for droppingoff the processed DUTs in the staging tray, the robotic arm 1104 maypick up from the staging tray a group of new DUTs to be processed atanother tier of burn-in stations for which the burn-in process is (or isabout to be) complete (2016, FIG. 20). Thus the process of exchangingnew DUTs for processed DUTs may be performed in turn for every tier ofburn-in stations of the system 1100, and may be repeated over and overagain for each tier of burn-in stations upon completion of each burn-inprocedure performed at a given tier of burn-in stations.

The DUT and the driver circuit at each burn-in station may perform inthe same manner as was described above in connection with the system100. (Indeed, since burn-in procedures are performed at each of thedocking locations of the system 100, those docking locations may also beconsidered to be “burn-in stations”.)

The system 1100 described with reference to FIGS. 11-20 may exhibit mostif not all of the advantages enumerated above with respect to the system100. In addition, the system 1100 may exhibit one or more of thefollowing advantages:

(1) The average cycle time required to exchange DUTs at each burn-instation may be substantially reduced, since only DUTs and not burn-inboards are transported, and several (e.g., six) burn-in stations areserviced in parallel. This may facilitate institution of burn-in testingfor larger samples or 100% of device lots with a shorter burn-in time.

(2) Wear and tear on the burn-in boards and the burn-in stations (andparticularly on the connection therebetween) may be substantiallyreduced, since burn-in boards are essentially permanently installed atthe burn-in stations and so are not docked to and undocked from theburn-in stations at each cycle.

In one embodiment, a device with on-die DFT as described above is partof a chipset incorporated in a computer system. The chipset may includea memory controller hub (MCH), an input/output controller hub (ICH), agraphics chip, etc. FIG. 21 shows an exemplary embodiment of a computersystem 2100. The system 2100 includes a central processing unit (CPU)2101, a MCH 2102, an ICH 2103, a flash memory device storing the BasicInput Output System (Flash BIOS) 2104, a memory device 2105 (e.g., adynamic random access memory or “DRAM”), a graphics chip 2106, and anumber of peripheral components 2110. The CPU 2101, the memory device2105, the graphics chip 2106, and the ICH 2103 are coupled to the MCH2102. Data sent and received between the CPU 2101, the memory device2105, the graphics chip 2106, and the ICH 2103 are routed through theMCH 2102. The peripheral components 2110 and the flash BIOS 2104 arecoupled to the ICH 2103. The peripheral components 2110 and the flashBIOS 2104 communicate with the CPU 2101, the graphics chip 2106, and thememory 2105 through the ICH 2103 and the MCH 2102. Note that any or allof the components of system 2100 and associated hardware may be used invarious embodiments of the present invention. However, it can beappreciated that other embodiments of the computer system may includesome or all of the devices.

Any or all of the robotic arms described herein may be considered to bea “transporter” since all transport DUTs and/or other items from placeto place within the systems 100 or 1100. This same term may also beapplied to any other device used in place of one or more of the roboticarms to transport a DUT, a burn-in board or a tray.

In some modified embodiments of the system 1100, DUTs are transportedindividually to each burn-in board/burn-in station, rather than beingtransported in groups. In such embodiments, the end effector of therobotic arm 1104 may be configured to “stomp” only one socket at a time,and to hold only one or only two DUTs at a time.

The several embodiments described herein are solely for the purpose ofillustration. The various features described herein need not all be usedtogether, and any one or more of those features may be incorporated in asingle embodiment. Therefore, persons skilled in the art will recognizefrom this description that other embodiments may be practiced withvarious modifications and alterations.

1-66. (canceled)
 67. A pair of burn-in stations, vertically disposedwith respect to each other, the pair of burn-in stations including afirst burn-in station and a second burn-in station, the first burn-instation being disposed above the second burn-in station and including afirst horizontally-extending support member adapted to support a firstburn-in board, the second burn-in station including a secondhorizontally-extending support member below the first support member andadapted to support a second burn-in board, the first support memberbeing at least partially hollow to form a duct to direct air from a fanto the second burn-in board.
 68. The pair of burn-in stations of claim67, wherein the first support member has an opening which faces towardthe second support member.
 69. The pair of burn-in stations of claim 68,wherein the first and second support members are substantially identicalto each other.
 70. The pair of burn-in stations of claim 69, wherein thefirst and second support members extend horizontally outward from afront side of a wall, and the duct leads from a rear side of the wall tothe second burn-in board, the rear side opposite to the front side. 71.The pair of burn-in stations of claim 67, wherein each burn-in stationincludes a docking location adapted to be coupled to an edge connectorof a burn-in board.
 72. A semiconductor device comprising: a thermalsensing circuit to monitor an internal temperature of the semiconductordevice; a terminal pin coupled to the thermal sensing circuit to providea signal external to the semiconductor device, the signal to indicatewhether the internal temperature exceeds a threshold temperature. 73.The semiconductor device of claim 72, further comprising a secondterminal pin coupled to the thermal sensing circuit to provide a secondsignal external to the semiconductor device, the second signal toindicate whether the internal temperature exceeds a second thresholdtemperature.
 74. The semiconductor device of claim 72, wherein thethermal sensing circuit includes: a thermal sensor; and one or morefuses coupled to the thermal sensor and programmed to set the thresholdtemperature.
 75. The semiconductor device of claim 72, furthercomprising: a plurality of gates; and a multiplexer coupled to theplurality of gates; wherein the thermal sensing circuit is coupled tothe multiplexer and is adapted to supply to the multiplexer a signalwhich is identical to the signal provided by the terminal pin, themultiplexer to select, in response to the signal supplied by the thermalsensing circuit, a clock signal out of a plurality of clock signalssupplied to the multiplexer to toggle the plurality of gates to generateheat internally to the device for burn-in.
 76. The semiconductor deviceof claim 75, further comprising: a state machine coupled to the gates toexecute a plurality of test modes during burn-in.
 77. A systemcomprising: one or more dynamic random access memory (DRAM) devices; anda chipset coupled to the one or more DRAM devices, the chipset includinga device, wherein the device includes: a thermal sensing circuit tomonitor an internal temperature of the device; a terminal pin coupled tothe thermal sensing circuit to provide a signal external to the device,the signal to indicate whether the internal temperature exceeds athreshold temperature.
 78. The system of claim 77, wherein the devicefurther includes a second terminal pin coupled to the thermal sensingcircuit and adapted to provide a second signal external to the device,the second signal to indicate whether the internal temperature exceeds asecond threshold temperature.
 79. The system of claim 77, wherein thethermal sensing circuit includes: a thermal sensor; and one or morefuses coupled to the thermal sensor and programmed to set the thresholdtemperature.
 80. The system of claim 77, wherein the device furtherincludes: a plurality of gates; and a multiplexer coupled to theplurality of gates; wherein the thermal sensing circuit is coupled tothe multiplexer and is adapted to supply to the multiplexer a signalwhich is identical to the signal provided by the terminal pin, themultiplexer to select, in response to the signal supplied by the thermalsensing circuit, a clock signal out of a plurality of clock signalssupplied to the multiplexer to toggle the plurality of gates to generateheat internally to the device for burn-in.
 81. The system of claim 77,wherein the device further includes a state machine coupled to the gatesto execute a plurality of test modes during burn-in.